¹Vollum Institute and ²Department of Oral Molecular Biology, Oregon Health Sciences University, Portland, OR, USA;
³Protein Structure Facility, Shriners Hospital for Children, Portland, OR, USA;
⁴EHS Center, Oregon State University, Corvallis, OR, USA
 

Abstract
      p300 is a phosphoprotein.  A major phosphorylation site of p300 in HeLa cells is serine 89, which is highly conserved among human and mouse p300 and CBP.  The kinase responsible for the phosphorylation of serine 89 (S89K) is a protein kinase C (PKC)-related kinase.  Phosphorylation at serine 89 by this kinase inhibits the p300 histone acetyltransferase (HAT) and transcriptional activities.  It also represses estrogen receptor (ER)-mediated transactivation that is potentiated by p300.  This inhibition of the ER activity through the phosphorylation of p300 at serine 89 implies a barrier to the cell cycle progression at G1, and thus correlates with  the physiological role of p300 in assisting cells to withdraw from the cell cycle and further inducing differentiation.

Department of Plant Pathology and Physiology, Clemson University, Clemson, SC 29634
 

Abstract
      Two-year-old dormant peach trees, with Red Heaven or Loring scion and Lovell or Nemaguard rootstocks, were grafted with twig tissue from healthy or infected sources of 4 Prunus necrotic ringspot virus (PNRSV) isolates.  Three trees of each of 4 scion/rootstock combinations were grafted with each source near the top and three on major roots.  Trees leafed out after 1-2 weeks in a greenhouse and weekly assays were carried out by ELISA.  PNRSV was first detected in leaves near the top of shoot-grafted trees 2-3 weeks after grafting.  PNRSV was systemic in this trees, including roots, at this time or 1-2 weeks later although virus was not detected in some branches until 6-14 weeks after grafting, or not at all in 1/4 of the branches.  PNRSV was not detected in any root-grafted trees or in trees grafted with healthy tissue.  Few differences were found among virus isolates or cultivars.  Thus, soil-borne transmission of PNRSV may not be an important means of natural spread.